Despite a plethora of neuropsychological and family-based research suggesting that Attention Deficit Hyperactivity Disorder (ADHD) is a neurobiologically-based disorder, studies attempting to define the neurobiological nature of ADHD have been few. As stated in the NIMH Consensus Development Conference on ADHD, there is a clear need to more basically define ADHD using basic research techniques. The proposed study will utilize the Multimodal Treatment Study of ADHD children (MTA) sample to recruit 30 ADHD parent-child dyads. ADHD dyads will consist of ADHD children and their concordantly-affected ADHD parents. Fifteen normal dyads will also be recruited who do not meet ADHD diagnostic criteria. Volumetric images using Magnetic Resonance Imaging (MRI) will be acquired on all dyads. In addition, all dyads will perform a series of neuropsychological tests while generic brain activation is assessed using functional MRI (fMRI). ADHD parent-child dyads will also participate in a repeated measures study examining functional neuroanatomical change in response to stimulant medication. Brain activation volumes and magnitudes in pre-specified regions of interest will be assessed. Between-group comparisons will evaluate structural and functional neuroanatomical differences between ADHD and normal parent-child dyads. Within-group analyses will compare ADHD patients' functional activation changes across placebo and active medication conditions. In addition, parent-child correspondences in neuropsychological performance, neuroanatomy, and brain activation will be examined within the two groups of dyads. This application is a collaborative R01 that will involve five sites. Participants will be recruited from three MTA sites: University Medical Center (DUMC), New York State Psychiatric Institute, and UC Berkeley. Imaging will be performed at corresponding imaging sites at DUMC, Weill Medical College of Cornell University, and Stanford University respectively.